Pressure swing reforming is a highly efficient and highly productive process for stream reforming hydrocarbons in a cyclic, packed-bed operation to produce synthesis gas.
In this process, the reforming stage involves preheating a first zone to a temperature in the range of about 700° C. to 2000° C. and then introducing a 20° C. to 600° C. hydrocarbon-containing feed, along with steam and optionally CO2 to the inlet of the first zone. Upon introduction of the reactants, the hydrocarbon is reformed into synthesis gas over a catalyst in this first zone. The synthesis gas is then passed from the first zone to a second zone, where the gas is cooled to a temperature close to the inlet temperature of the hydrocarbon feed. The synthesis gas is recovered as it exits the inlet of the second zone.
The regeneration stage begins when a gas is introduced to the inlet of the second zone. This gas is heated by the stored heat of the second zone to the high temperature of the zone and carries the heat back into the first zone. Finally, an oxygen-containing gas and fuel are combusted near the interface of the two zones, producing a hot flue gas that travels across the first zone, thus re-heating that zone to a temperature high enough to reform the feed. Once heat regeneration is completed, the cycle is completed and reforming begins again.
An advantage of this process is the ability to operate the reforming stage at a higher pressure than the regeneration stage, thus creating a pressure swing, and producing high pressure synthesis gas.
The general stoichiometry for the steam reforming of a hydrocarbon, as illustrated for methane, is:CH4+H2O→CO+3H2  (1)
In copending U.S. patent application Ser. No. 10/771,919 a process is provided for generating hydrogen at improved thermal efficiencies and that is particularly adaptable for environments requiring hydrogen at relatively high pressures for refinery processes, for direct use as a fuel and for distribution. The inventive process integrates pressure swing reforming in which synthesis gas is produced with the water gas shift reaction and hydrogen separation under conditions sufficient to yield high pressure hydrogen at improved thermal efficiencies.
The general stoichiometry for the water gas shift reaction is:CO+H2O→CO2+H2  (2)
In the disclosed process the reforming phase of the pressure swing reforming is conducted at relatively high pressures, for example, from about 10 to 100 bar and the product synthesis gas is subjected to a water gas shift reaction and a hydrogen separation step at substantially the same pressures thereby providing high pressure hydrogen. In one embodiment flue gas from the pressure swing regeneration stage is used to power a gas turbine for power and steam generation.
It is an object of the present invention to generate power with a gas turbine, which utilizes pressure swing reforming under conditions that facilitate CO2 capture. The capture of the CO2-product of fuel combustion in power generation is of interest for the recovery of CO2 for use as chemical feedstock, as agent of enhanced oil production, and for the purpose of sequestration, the disposal of CO2 for purposes of mitigating the climate impact of fossil fuel use. It also is an object of the present invention to provide a means to achieve power production with CO2 capture that under conditions that result in a minimum loss of power production efficiency. Present technologies known in the art for CO2 capture in power generation are both expensive and inefficient. For example, separating CO2 from the dilute fluegas of a power plant has an efficiency loss reflected in a fuel penalty greater than 16% (i.e. requires 16% more fuel for same power output); separating CO2 from the concentrated syngas in a coal gasification combined cycle power plant carries a fuel penalty over 14%. Combining conventional steam reforming, partial oxidation or autothermal reforming with gas turbine power generation can result in a fuel penalty of 20% or more.
Another object of the present invention is to maximize one of power or hydrogen production under conditions that facilitate CO2 capture.
Other objects of the invention will become apparent upon a reading of the detailed description of the invention which follows: